In this post I have explained a simple, accurate, high torque treadmill motor speed controller circuit which may be effectively installed in similar units for acquiring PWM controlled variable speed feature. The idea was requested by Mr. Samuel.
Technical Specifications
I've a treadmill whose power failed completely...it had been imported from china and it's like they can't help after negotiating with them..guarantee is only meant in their x-try.
So, am asking, how would you assist me in designing a power supply that will control speed and change of direction of the treadmill movement as well. I'm and forever will be glad for your work.
Looking into the specs of the unit, the switching relays are specified with 10A ratings. I also had a view of the motor and it was written 180Volts on it.
This is the information i got sir. They also had a cautionary notice that the T.Mill shouldn't be run beyond 2hrs continuously. I hope I've given the best for the best.Thanks sir. Stay blessed now and forever! best moments!
The Design
Here's a simple PWM based motor speed controller circuit which can be used for controlling a treadmill speed right from zero to maximum.
The circuit also provides an instant bidirectional stop and reversal of the motor rotation by a single flick of a given switch.
Another interesting feature of this circuit is its capability of sustaining and balancing optimal torque even at lower speeds ensuring a continuous working of the motor without stalling it during extreme low speeds.
The circuit of the proposed treadmill motor speed controller may be understood with the help of the following points:
Here the two 555 ICs are configured as PWM generator/optimizer for acquiring the required speed control of the connected motor.
Circuit Operation
IC1 works as a frequency generator and is rigged at around 80Hz, any other value would also do and is not anyway critical.
The above frequency from pin#3 of IC1 is fed to pin#2 of IC2 which is wired as a standard monostable. IC2 responds and starts oscillating at this frequency, forcing equivalent triangle wave frequency at its pin2/6.
The above triangle waves is instantly compared by the set potential at pin#5 of IC2 creating an equivalent level of chopped PWM at its pin#3
The preset or a pot positioned at pin#5 of IC2 forms a potential divider network for a selectable fixing of any voltage from zero to maximum supply voltage at pin5 of IC2. This level is directly translated through optimized PWMs at pin#3 of the same IC as explained above.
The PWMs are fed across two sets of NOT gates via an SPDT toggle switch.
The NOT gates which act as inverters provide the feature of instant toggling of the motors rotational direction by a mere flick of the SPDT switch.
The resultant PWMs from the selected NOT gates finally reach the transistorized bridge network that holds the motor between them for implementing all the specified features discussed above.
These transistors should be rated as per the motor specifications, and the voltage across this bridge should also be as per the motor requirements.
Video Clip:
Simplified Design
If you do not wish to have the reverse forward facility, then you can much simplify the above design by eliminating the lower section of the circuit entirely, as shown below:
The 10K pot can be used for the speed control, while the 220uF determines the soft start feature. Increasing the 220uF value increases the soft start effect and vice versa.
Controlling Through an External Power Supply
The above design could be also modified for enabling motor speed control through an external variable power supply, as shown below.
Pin#5 can be seen driven from an external 0 to 10V variable power supply, for example from a LM317 based power supply
If you do not wish to use an external power supply, the above treadmill speed controller design could be simplified even further, by adding a 1k pot at pin#5 of IC2, as demonstrated below:
The 1k pot will allow you to adjust the treadmill speed from 10% to 90%, and the C4 value could be experimented to add a nice soft start to the treadmill motor during the switch ON.
Construction Guide
Power Supply Section
15V DC Supply:
Ensure that the input power source delivers a stable 15V DC, because it is critical for the 555 timers and the IRF540 MOSFET operation.
Use a well-filtered power source to avoid the noise interference.
Zener Diode (D1 - 2.7V):
Provides a fixed reference voltage for the base of T1 (BC557 transistor) which gives stable operation.
PWM Generator (IC1 - 555 Timer)
The first 555 timer (IC1) is configured as an astable multivibrator, to generate a pulse-width modulated (PWM) signal.
Pin Connections:
Pin 1 (GND): Connect to the ground.
Pin 8 (Vcc): Connect to +15V supply.
Pin 4 (Reset): Connect to +15V to enable the IC.
Pin 5 (Control Voltage): Add a 10nF capacitor (C2) to ground to stabilize the PWM signal.
Pin 3 (Output): Outputs the PWM signal to the base of T1 (BC557 transistor) via R4.
Frequency Control:
Use R1 R2, and C1 to set the frequency of the PWM signal.
Formula for frequency:
f = 1.44 / [(R1 + 2R2) * C1]Where:
R1 = 180kΩ
R2 = 100kΩ
C1 = 100nF
PWM Adjustment (1kΩ Potentiometer):
The 1kΩ potentiometer varies the duty cycle of the PWM signal allowing the speed control of the treadmill motor.
Soft Start and Motor Driver (IC2 - 555 Timer)
The second 555 timer (IC2), is configured as a monostable multivibrator to implement the soft start feature.
Pin Connections:
Pin 1 (GND): Connect to the ground.
Pin 8 (Vcc): Connect to +15V supply.
Pin 4 (Reset): Connect to +15V to enable the IC.
Pin 5 (Control Voltage): Add a 10nF capacitor (C3) to ground.
Pin 3 (Output): Drives the gate of the IRF540 MOSFET.
Soft Start Capacitor (C4 - 10nF):
This capacitor determines, the ramp-up time for the soft start feature.
Larger values of the C4 increases the soft start time.
Adjust C4 using the formula:
t = 1.1 * R6 * C4Where:
R6 = 10kΩ
C4 = Soft start capacitor
Motor Connection:
The motor is connected to the drain of the IRF540 MOSFET with the source connected to the ground.
D5 (1N4007): Protects the MOSFET from back the EMF generated by the motor.
Working Principle
PWM Speed Control:
The duty cycle of the PWM signal generated by IC1 provides the average voltage applied to the motor.
Adjusting the 1kΩ pot, changes the PWM duty cycle effectively, controlling the motor speed.
Soft Start:
When the circuit is powered ON, the IC2 gradually increases the gate voltage of the MOSFET due to the charging of the C4.
This ensures that motor starts smoothly without jerks.
Overvoltage Protection:
The 2.7V zener diode (D1) ensure the PWM output voltage doesnt exceed safe levels for the transistor T1.
Relevant Calculations
Frequency of PWM Signal (IC1):
f = 1.44 / [(R1 + 2R2) * C1]For the given values:
R1 = 180kΩ
R2 = 100kΩ
C1 = 100nF
Substituting:
f = 1.44 / [(180k + 2 * 100k) * 0.1µF]
f ≈ 34.3 Hz
Soft Start Time (IC2):
t = 1.1 * R6 * C4For the given values:
R6 = 10kΩ
C4 = 10nF
Substituting:
t = 1.1 * 10k * 10n
t = 0.11 msIf a larger value for the C4 is chosen (e.g 1µF):
t = 1.1 * 10k * 1µF
t = 11 msAssembly Tips
Use a Heat Sink for the IRF540:
The MOSFET can heat up under heavy motor loads so Attach an appropriate heat sink.
PCB Design:
Keep the ground connections of the IC1, IC2 and the motor driver separate to avoid noise.
Testing:
Test the PWM output with the multimeter or oscilloscope before connecting the motor.
Safety Precautions:
Ensure proper insulation for all tthe high-current connections to prevent short circuit.
Using A Dimmer Phase Chopper Circuit
As rightly suggested by one of the dedicated readers of this blog, Mr. Ivan, a 180 V treadmill motor can be simply controlled through mains phase chopping concept, normally incorporated in all commercial dimmer switches for regulating home fan speed.
Shown below is a modified dimmer switch circuit design which can be effectively used for regulating a 180 V treadmill motor from zero to max:
Please make sure to use a non-polar capacitor for the one shown between the bridge rectifier.
Use the following type, 10 in parallel
10nos of 0.47/400V in parallel will make 47uF/400V non polar capacitor which may work like a decent filter capacitor for the motor.
Questions & Answers
Hi, Could you explain how a constant torque at low speeds is achieved? My treadmill bogs down slightly with each step when I get below about 1.2mph.
Constant torque is achieved by the use of PWMs which prevent the devices from unnecessarily heating up yet allowing them to conduct fully during the ON states of the devices.
So it's like allowing the devices to conduct fully with full power yet only at the desired slower speeds by breaking their conduction many number of times per second.
Hello
My treadmill motor is rated for 130VDC and 15a. I plan on using 120vac(line voltage) and a bridge rectifier to power the motor. What type of transistors would I use for T2-T5? I don't recognize the symbol you used. IRF540 mosfet is only 100v, I think. any advice is welcome.
Also, what is the symbol just left of C1? I apologize for my lack of knowledge.
Hello,
You can use MJ11021(PNP) MJ11022 (NPN) for the transistors
It indicates the (0) volt line or the negative volt line.
I'm putting together a shopping list for this project. 1/4 watt metal film resistors would work, right?
C3 is listed as 1uf, what voltage and style of capacitor should i get? The other caps I was going to buy 50VDC ceramic disc. My motor is rated at 130VDC 15A, i was going to power the motor with 110VAC thru a bridge rectifier, any ideas on what transistors to buy? IRF540 is only 100volts One last thing, what is the symbol just left of C1? I apologize for my lack of knowledge.
BJTs are easier to handle than mosfets, so it's better to use BJTs here.
Thank you for your replies. I have all the part numbers figured out and I am excited to build this circuit. This is an amazing site and appreciate the time you dedicate to helping others. Thank You.
You are welcome!
Thanks for the great design! Why are the BJTs better here, as I understand BJTs are preferred for low current applications, while MOSFETs are for high power functions.
Thanks,
Matt M
If the requirement is above 30 amps mosfets could be preferred…mosfets require stricter parameters while configuring compared to BJTs therefore sometimes become difficult to handle.
however in the above design mosfets could be used since the configuration does not demand a high side driver due to the involvement of both n/p mosftes..
Thanks for this fantastic circuit diagram. I'm new to electronics so please excuse me if these are dumb questions. Would there need to be any programming done to make this work or does the hardware do all that automatically? Also, I wouldn't need the reverse feature and a simpler circuit would definitely be easier for a beginner like me. Could you show us what this circuit would look like without the components necessary for the reverse feature and how I could make this work using 110vac i.e. Where would the ac come in and where would it be rectified? Thanks again!
Thanks very much Michael, no programing is required for the devices all the ICs come preprogrammed, just have to wire them up in the shown manner.
If you are not interested in the reversing feature the circuit definitely becomes much simpler as shown in the following image:
1.bp.blogspot.com/-jONLYQ8Ehro/UkD_gzAjA-I/AAAAAAAAFSk/nt6vxMDF9RU/s1600/ELC+circuit.png
ignore the four diodes shown at the top which was drawn for some other similar application need.
the mosfet upper lead which is drain needs to be connected with the motor negative, while the positive of the motor will connect with the 110V DC or whatever may be the motor operational voltage spec.
The circuit would however need to be powered through a 12V AC/DC adapter specified to take the input from a 110V AC, nowadays such adapters are suited for any input right from 85V AC to 285V AC, so it won't be much of a concern
The shown pot could be used for the required speed control.
Excellent. Thanks!
what is D1 is it a zener diode
yes it's a zener diode.
im sorry one more, R4 is that 2.2k or 2002 ?
it's 2.2k
Many thanks Sir for this publication.
I'm sorry for dump questions but I'm newbe to electronics.
Will this work with my 240VDC/12A motor?
How many of this CD4049UBE CD4049 4049 IC Hex Buffer/Converters do I need to order?
Regards,
Wes
My pleasure! yes it'll work with the specified motor, you'll need to use high voltage BJTs for it as given in the following datasheet:
https://www.homemade-circuits.com/2014/04/mj11021pnp-mj11022-npn-high-voltage.html
Only one 4049 IC is required for the above design
Thanks a lot!
Dear Swagatam, many thanks for your fast replies.
I’ve managed to put everything together and pluged in. Unfortunatelly when my treadmill motor (220VDC/3.5hp)
started to turn a smoke come out from one of the BJTs.
Now it looks like all four of them (mj11021pnp-mj11022-npn) has gone, cos I can’t see any reading between base-collector, emitter when testing them.
What I’ve noticed afterwards that it was a bad solder between R6 and bases of T2,T3.Virtually no connection at all. Also I’ve used 1N4744 as a D1.
What do you think Sir. Any suggestions?
Regards, Wes.
Dear Wes,
A bad solder won't cause a burning problem according to me, I think the treadmill motor could have exceeded the max amp rating of the BJTs,
Replace the circuit with new transistors and try operating the treadmill without any load, check the response,
the other reason could be wrongly configured BJTs
….1N4744 are zener diodes and will never work here, you'll have to use rectifier diodes such as 6A4 etc.
this could be an issue too
Many thanks Swagatam.
New high voltage transistors just been ordered. You're right. After closer examination it looks like BJTs were wrongly configured. This cause them to burn.
So do you think that I could use four 6A4 rectifiers in the bridge instead of 1N4001 as it is in your cuircuit?
Talking about Zenner diodes, I'm using 1N4744 instead of 2v7 as a D1 which is a Zenner diode in your circuit. I don't use them in the bridge.
Regards Sir,
Wes
OK Wes, that's good! yes 6A4 is the minimum requirement for the bridge diodes, 1N4001 will not do as these will blow of due to the high motor back emf.
I mistakenly thought that you had used the zener in the motor bridge circuit,….surely it will do in place of the shown 2.7V zener
Many thanks Sir. Now it looks very promising.
Regards,
Wes
You are welcome!!
Mr. Majumdar, I have a similar problem. I have a treadmill which controller chip has failed and now i would like to build independent control of the motor. It is PMDC (Permanent-magnet DC) motor, 180V, 6.8A. I want to control it's speed from zero to max by powering it from 220V AC power grid. Can you give some circuit similar to the above one, but for 220V AC, please?
Hi Ivan, you can try the following simple design
https://www.homemade-circuits.com/2012/05/make-this-pwm-based-dc-motor-speed.html
Just make sure that the circuit supply is acquired from a 12V AC/DC adapter while the motor terminal from a 180V Dc (+) source
The (-) of the 180V must be made common with the (-) of the 12V supply or the (-) of the circuit
The 180V could be achieved through a half wave rectification using a single 6A4 diode and filtered using a 10uF/400V capacitor.
The MOSFET should be an IRF840
Thanks for the reply, Mr. Majumdar, but the circuit you offer uses PWM. How about just changing the gate voltage in order to control the drain current? Is this possible and which way is the best?
Hi ivan, It's not possible to control a mosfet drain load with a varying gate voltage, PWM is the easiest and the most ideal way of achieving the intended speed control through a mosfet.
Thanks, I'll do it!
Hi, Mr. Majumdar, I did exactly as you told me – a half-wave rectifier with 6A4 diode and a 10uF/400V capacitor, but the voltage between the poles of the capacitor is 325V DC!
Hi Ivan, it's showing the peak voltage, once connected to the load the voltage will come down to the specified level, however still it could be not so safe to apply the pulsating peaks to the motor, so I think you will have to get a suitable auto-transformer designed from a transformer maker. Tell him to design a transformer which would be able to supply 150V/6amp from 220V….this output can be then bridge rectified and filtered to acquire the required 180v for your motor.
Sorry for my last post, I knew that this is the peak value of the voltage formed by the capacitor, but the post was already on its way. At all I intend to use this circuit:
2.bp.blogspot.com/-wJnI3vNWGoo/UoxAV_X6LyI/AAAAAAAAFxU/7NZJ4A2bg88/s1600/treadmill+motor+speed+controller+circuit.png
I have also some differences – I need one direction and have 180V DC motor at 2.2HP (that's 1640W of power). It seems that the circuit must be without those NOT gates because of the single way rotation and I'll need only 2 power transistors (in parallel oor in sequence). I don't know only what should be those Darlingtons?
Yes, you are right the NOT gates won't be required in the referred diagram.
For the transistor you can simply use a single high voltage Darligton transistor such as ST901T with pin3 of IC2 for the required implementation.
Just a single ST901T?! I have 1640W of power which makes around 9A of current at 180V and the Icmax of ST901T is just 4A?! The motor will not be loaded at the maximum power rate but still isn't 4A too less? How about 2 or even 3 ST901T's in parallel?
sorry it won't work, I seems I missed the amp spec of the device.
you can either search for a suitable single device or connect many of these in parallel, just make sure all of these are mounted over a single common heatsink.
Hi any possibility a ready made controller can be purchased. I do not have a knowledge about electronics and am desperate in powering up my treadmill.
Hi, I wish I could help by doing it for you, but I am sorry, presently that looks difficult due to lack of time.
Hello, mr Majumdar, I have something much simplier in view with respect to 180V DC treadmill motor control powered from 220V AC grid. The parameters are:
– 220V AC power grid
– 180V permanent magnet DC motor 7Amps motor
– main control element a SCR (thyristor) simultaneously acting like rectifier and control element with phase controlling circuit
– a capacitor in parallel after the thyristor acting simultaneously like smoothing element for the phase-cutted sine and voltage-raising capacitor (just like in the last circuit you offered me).
– a SCR control circuit that uses phase-cut method – cutting the sine at different angles in order to get different voltage values above the motor.
I think it will be much simpler than the two 555 timers PWM and Darlington stages.
Best regards!
Hello Ivan, yes that's a smart idea, since the load is 180 V rated using a dimmer switch circuit as the speed controller is definitely possible, the motor output will only require a bridge network and filter capacitor for the AC to DC conversion.
If possible I'll try to update the design in the above article soon.
Your work will be highly appreciated because I'm trying to run this treadmill for 4 months. An easy-to-build and cheap solution will be more than a good result for me.
I have updated the required diagram above, please check it out.
Thanks, mr. Majumdar, one more question, what diameter should the iron core of L1 have?
Thanks Ivan, The diameter of the core could be such that it accommodates the 200 turns comfortably, it could be done over an iron bolt or screw…but the diameter of the wire should be more than the indicated 0.6 mm since the motor is rated to carry high currents…a 1.5 mm could be tried initially.
Hi, Mr.Majumdar, the dimmer circuit simply does not work, I did 3 times, the load works always at the grid's voltage (220V), no matter the potentiometer setting. All the elements are the same as required, the circuit has been checked maybe 30-40 times, everything is correct but it doesn't work. I also did a circuit with PWM and a MOSFET, the same fails everytime at nearly half turned potentiometer and the engine is even at idle.
I never imagined that controlling the speed of a DC motor can be so difficult!!!
Hi Mr. Ivan the first circuit has been tested by me and it worked right at the first shot, so it surely works, but all these can be difficult for any newcomer i can understand that.
in the second circuit, remove the motor, the bridge diodes network..verify the circuit using an AC lamp as shown in the following lamp, if this doesn't work will mean your circuit is faulty somewhere
1.bp.blogspot.com/-s2Fe-xTv4YA/T4V-Z597HLI/AAAAAAAABFk/mafeMQ6JYm4/s1600/How+to+Control+AC+Motor+or+a+Ceiling+Fan.jpg
connect a 100 watt bulb in place of the "AC motor" in the above link
Mr. Majumdar, I didn't say anything about your first circuit, at least my was with MOSFET stage unlike yours. As for the second one, I tried alll the things you said – removing the engine and the bridge and using a 100W lamp as AC load. The result was the same. Anyway . . . . Now I found another circuit in one of our old elctronic magazines (I'm from Bulgaria). Unlike your second circuit it uses thyristor (SCR), not triac.
postimg.org/image/49kyj0io3/
It's used for drill machines and can power a engine up to 800W. The list of elements is in bulgarian, that's why I'm not posting it here. As in the circuit above, a bridge rectifier and a smoothing capacitor should give my treadmill DC motor what it needs . . . . . I hope.
Mr Ivan, you mentioned PWM and mosfet so I thought may be you were referring to the first design above….
anyway the second circuit is a very basic fan dimmer switch design that we use in our homes for controlling fan speeds or light intensity….i have tested the circuit thoroughly and have one installed in my house….so if an AC load is not working in your circuit then definitely there's something incorrect in your circuit assembly.
The image that you ahve provided will controll speeds upti 50% only and will create lot of jerk at lower speeds….i already have a similar design posted in my blog here:
https://www.homemade-circuits.com/2012/01/how-to-make-versatile-closed-loop.html